FDA clears first treatment for Prader-Willi syndrome

Soleno Therapeutics' Vykat XR has become the first FDA-approved treatment for Prader-Willi syndrome (PWS), a rare genetic disorder that causes excessive appetite and obesity.

Vykat XR (diazoxide choline) has been cleared to treat hyperphagia – an intense and incessant urge to eat that can lead to dangerous weight gain – which is the signature feature of PWS, caused by mutations to groups of genes found on chromosome 15.

The once-daily, oral drug can be used in PWS patients aged four years and over who have hyperphagia, which is virtually all people with the disease and the leading cause of mortality. The disorder can also cause other issues including learning difficulties, behavioural problems, restricted growth, and a shorter life expectancy.

There are around 50,000 people diagnosed with PWS in the US and up to 400,000 worldwide, according to the Redwood City, California-based company, with an estimated 10,000 patients in the US eligible for treatment.

Soleno has said it intends to launch Vykat XR in April, with the price defined by the weight of the patient and set at $5.92 per kilogramme. Based on the average weight of subjects in the company's pivotal clinical trial, it estimates that the average cost of treatment will be $466,200 per year.

That phase 3 trial showed that treatment with Vykat XR was able to reduce hyperphagia – although, not by a statistically significant degree at the primary endpoint – and improved several other symptoms such as aggressive and destructive behaviours, fat mass, and other metabolic parameters.

After extended follow-up, the difference reached significance, however, and individuals who switched from Vykat XR to placebo in a 16-week withdrawal phase – after an average of more than three years on the drug – demonstrated a statistically significant worsening of hyperphagia compared with those who remained on it.

Side effects that occurred more frequently than placebo included excess fair growth, fluid retention, high blood sugar levels, and rash.

Stacy Ward, chief executive Officer of the PWS Association USA, said that the approval represents a "monumental step forward in addressing the longstanding unmet needs of individuals living with PWS and their families."

Soleno has previously said it plans to file for approval of Vykat XR in Europe in the first half of this year, estimating that there are approximately 9,500 diagnosed PWS patients in the four largest EU markets, as well as the UK. It remains well-funded for the rollout, ending 2024 with more than $318 million in cash reserves.